Field of the Invention
The present disclosure relates to a prism block as well as an optical unit and a scanner optical system, each of which employs the prism block.
Description of the Related Art
In a reduction optical system, a long optical path needs to be provided between a target object and an image capturing element. Conventionally, this long optical path is folded through reflections by mirror surfaces, thereby achieving a reduced size of an optical unit.
However, as image capturing elements have been reduced in size in recent years, optical units are required to be further reduced in size. In view of such a requirement, in some cases, there is used an optical unit configured to cause multiple reflections of a light flux in a prism block.
Regarding such a prism block, Japanese Laid-Open Patent Publication No. 2000-111799 discloses an image formation optical system having a first prism and a second prism. Specifically, the first prism reflects an entered light flux at its first to fourth reflection surfaces, then the reflected light exits from the first prism and enters the second prism. At least one surface of each of the first prism and the second prism has a rotational asymmetrical shape to provide the light flux with power and correct an aberration resulting from eccentricity thereof.
Regarding a technique of reducing the size of an optical unit using a prism block, Japanese Laid-Open Patent Publication No. 10-178526 discloses a configuration in which reflected light from a document enters a prism, the light thus having entered via an entrance surface thereof is reflected by each reflection surface at least once before exiting from an exit surface, and the light is guided to a CCD via a lens to scan image information of the document.